After weeks of searching, the Mars rover Curiosity's science and engineering teams have selected a fine-grained slab of Martian rock as the candidate target for the first rock drilling on Mars, a significant first in planetary exploration.

Meanwhile 6,300 miles away, the nearly 9-year-old rover Opportunity continues to amaze. The latest analysis of Opportunity data by the rover's science team adds more evidence that life could have formed on Mars.

Nearly 210 million miles from Earth, Curiosity and Opportunity continue to inspire, educate, and fulfill the scientific promise of their missions.

In addition to selection of a drilling target, the Curiosity team is studying an intriguing geologic find at the Yellowknife Bay area covered with light-toned flat rocks (image above).

Rising out of the ground is an edge-on "snake like" protrusion of rock at a 90 degree angle to the flat exposed rocks that surrounds it and could have been formed in a lake bottom. Dubbed Snake River "It's one piece of a puzzle," said mission project scientist, John Grotzinger of Caltech. "It has a crosscutting relationship to the surrounding rock and appears to have formed after the deposition of the layer that it transects."

A graphic diagram of the 60 lb. Curiosity turret annotates its science hardware. The turret, with its 3 pronged drill, has come into its own over the last month performing rock triage to find drilling target. Credit: NASA/JPL

The Curiosity teams do not yet have Jet Propulsion Laboratory management permission to use the drill and when that drilling will actually start has yet to be decided.

That will come after additional engineering and scientific study of the rock candidate, which could be rejected if its suitability for drilling fails to pass final assessments.

The rock was selected Jan. 7 based on data about its composition, hardness, likelihood of generating powder needed to coat internal surfaces, and the safety of the drilling mechanism and rover when drilling this particular slab.

The candidate selection itself was a significant milestone, although that was kept secret for days for unknown reasons by the science team and JPL Public Affairs.

This is where flat, light-toned rocks, possibly formed under water, have been overlaid in part by much darker material that could be volcanic basalts, which in turn have been overlaid in places by alluvial fan material.

Sources say the drilling candidate is not the same rock dusted off Jan. 6 on Sol 150 during the first use of the rover's Honeybee Robotics Dust Removal Tool (DRT).

This image from the Mars Hand Lens Imager (MAHLI) on NASA's Mars rover Curiosity shows the patch of rock cleaned by the first use of the rover's Dust Removal Tool (DRT). The area is about 1.85 in. x 2.44 in, (47 millimeters by 62 millimeters). MAHLI took this Jan. 6 image from a distance of about 10 inches (25 centimeters) after the brushing was completed on this rock target called "Ekwir_1."

As geologist Robert C. Anderson, of the Curiosity Surface Sampling System (SSS) Team told CuriousMars earlier, "the selected candidate will first be compared with terrestrial rocks to provide an idea of how hard the rock is and how it compares to what has already been tested".

Anderson has spent years putting together an entire catalogue of rocks from very soft clays to hard basalts.

For the last 5 years, he has been running samples of those rocks through a Curiosity engineering drill rig to see how effectively rock powder from the percussion drill bit is augured up the hollow walls of the bit to a storage can above. "So we have an idea of what the drill is going to do," he told CuriousMars.

"We are going to look at the target rock, determine if its characteristics are similar to one of the catalogued rocks, then take the most similar cataloged rock and put it in the drill testbed at JPL, then try it at different settings," said Anderson prior to selection of the finalist.

From those tests now underway, the teams will determine a conservative drill setting and then present that to engineering and Curiosity project management for discussion and eventual approval to actually drill.

"We have six levels of percussion and we will be very careful with the initial rocks we drill," said Anderson. He said drilling is likely to start with just "tap, tap, tap" kind of impacts gradually building to heavier and more frequent blows of what is more of a rotating percussive chisel than drill.

The rock's fine grain size is important to generating the kind of powder needed to first clean the drill system of potential contaminates acquired during final assembly, launch and the 8-month cruise to Mars.

The first 3-5 drilling operations will be used to clean the drill. The selected rock will be drilled and dumped at least three times. This includes transport of the sample into the circular can atop the bit that holds the powdered sample.

Curiosity's complicated drill bit must first be coated with Martian rock dust to flush out any Earthly contaminates. The rover also carries two backups drill bits. Credit: NASA/JPL/Caltech

Each time the drill system will be vibrated to ensure the wall of the system is coated with Martian dust. Once that has been completed, rover arm motions will use gravity to dump a fourth or fifth sample into the adjoining CHIMRA collection and handling system that will filter the sample to the 150 micron size particles needed for the SAM instrument or 1 millimeter size particles adequate for CheMin.

It may still take another week or two for the drilling operations to get underway. The Curiosity team is being extremely careful because the success of the mission rides in large part on the performance of the drill.

Home of the smectites: With a little help from the Compact Reconnaissance Imaging Spectrometer for Mars(CRISM) onboard the Mars Reconnaissance Orbiter, Opportunity and the MER science team have determined that the Whitewater Lake rocks on Matijevic Hill are harboring smectite, the clay minerals they were hoping to locate. These rocks, which form a distinctive unit or layer in the rim of Endeavour Crater, are distinguished by 'splashes' of darker coating and tiny little veins. Image credit: NASA / JPL-Caltech / Cornell / ASU

On the other side of the planet, the Mars Exploration Rover (MER) Opportunity and her science team homed in on the smectite clay minerals they came looking for at Endeavour Crater, chalking up another plum scientific achievement even before the New Year rang in and Curiosity got her drill cranked up.

The smectites (pronounced smek-tights) are clay minerals in a class of water-altered minerals known as phyllosilicates. They are harbored, Squyres and Arvidson say, in bright, flat, recessed rocks marked with splotches of a dark coating and tiny veins, which the team calls Whitewater Lake outcrops. Named after the first such bright, flat rock the rover checked out last September, the Whitewater Lake rocks are also sprinkled with the new kind of small spherules, dubbed "newberries" that Opportunity first discovered at the base of Matijevic Hill last August. These rocks, the scientists noted, belong to a distinctive single unit or layer forming the rim of the big crater.

"There is no longer really any doubt in our mind that Whitewater is the clay-bearing unit," Squyres told CuriousMars.

Finding the smectite - rather to be more precise, locating the smectite - is a big scientific deal for Opportunity and the MER mission. The main reason is that "clay minerals form under more neutral water conditions," Squyres said simply.

From Eagle to Endeavour: The yellow line on this picture of Endeavour Crater, taken by Malin Space Science Systems' Context Camera onboard the Mars Reconnaissance Orbiter (MRO), shows the course that Opportunity charted from Eagle Crater, where the rover landed in January 2004 (at the upper left end of the track) to a point about 3.5 kilometers (2.2 miles) away from the rim of Endeavour Crater. The rover arrived at the rim of 22-kilometer (14-mile) diameter hole in the ground in August 2011, after a three-year journey from Victoria Crater. Image credit: NASA /JPL-Caltech / MSSS

The neutral to alkaline water in which clay minerals form is different than the highly acidic past water for which Spirit and Opportunity both found substantial evidence. While there are a number of different geologic ways that clay minerals form, "they do not form under highly acidic conditions," Squyres pointed out. Therefore, the presence of clays speaks of a water environment "with a chemistry more favorable for life" than a high acid chemistry. "Our hypothesis is: if there are clay minerals, the water was less acidic and therefore more conducive to life," summed up Arvidson.

Opportunity has been exploring the Cape York segment of the western rim of Endeavour Crater, a 22-kilometer (13.7-mile) diameter hole in the ground, since arriving there in August 2011. After waiting out its fifth Martian winter from a parked location on the northern end of the Cape York, the rover moved on last May and arrived at the foot of Matijevic Hill, a rise along the inboard side of Cape York, in late August 2012.

Both Squyres and Arvidson are in solid agreement that the smectite deposits are in the Whitewater Lake unit. And while both have announced coming to that conclusion - here and in data presented at the recent American Geophysical Union (AGU) meeting last December in San Francisco - it is an inferred finding that still has to meet muster in the traditional peer review process before it's officially official.

Opportunity and MER science team members were able to successfully ground-truth the smectites as quickly and efficiently as they did because of critical data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard the Mars Reconnaissance Orbiter (MRO). This visible-infrared spectrometer searches for mineralogic indications of past and present water on Mars, and in 2008 it detected the specific signature for smectite from Matijevic Hill, as well as other areas on the rim of Endeavour Crater.

Actually, CRISM's detection of smectite at Endeavour Crater was one of the prime drivers in the team's decision back in September 2008 to head out from Victoria Crater on what turned out to be a three-year, 21.5-kilometer (13.35-mile) journey across the Meridiani Plains. "Finding the clay minerals was our big objective," recalled John Callas, MER project manager, at the Jet Propulsion Laboratory (JPL), home to all the American Mars rovers.

CRISM sees red: The yellow line on this picture of Endeavour Crater, taken by Malin Space Science Systems' Context Camera onboard the Mars Reconnaissance Orbiter (MRO), shows the course that Opportunity charted from Eagle Crater, where the rover landed in January 2004 (at the upper left end of the track) to a point about 3.5 kilometers (2.2 miles) away from the rim of Endeavour Crater. The rover arrived at the rim of 22-kilometer (14-mile) diameter hole in the ground in August 2011, after a three-year journey from Victoria Crater. Image credit: NASA /JPL-Caltech / MSSS

Given that CRISM actually discovered the presence of the smectite clay minerals, Opportunity's assignment was to ground-truth their location, to characterize their host rocks and settings, and determine the geologic context. But with its two mineral detecting instruments - the miniature thermal emission spectrometer (Mini-TES) and the iron-detecting Mössbauer spectrometer - no longer working, the rover "cannot independently confirm the mineralogy of the Whitewater Lake outcrops," Arvidson reminded. So, the scientists - with data collected by CRISM in hand, along with the rover's multitude of images - had to deduce the location of the smectite.

Arvidson, who is also a co-investigator on the CRISM team, spent about a year carefully mapping that instrument's clay-bearing signature data, pixel by pixel, onto a HiRISE map and then overlaying it onto the exposures of Whitewater Lake that Opportunity was seeing on the ground. The signature area [on Matijevic Hill] as seen from CRISM "correlates one-to-one" with the outcrops of Whitewater material, he told CuriousMars recently, confirming research presented last month at the AGU meeting. "With Opportunity, we're now basically characterizing the properties and geological setting of the smectite based on the CRISM data," he said.

By any account, this is remarkable science coming nearly nine years into a mission that was only scheduled to last three months. And there's more.

The Whitewater Lake unit just so happens to be, Squyres noted, the oldest rock layer Opportunity has ever seen. "We now strongly suspect, but have not conclusively proven, that the Whitewater Lake [unit] is older than the Shoemaker Formation, and that the Shoemaker Formation breccias were deposited on top of this Whitewater unit," Squyres said. "These are the oldest rocks seen by this rover, and they are definitely the ones that contain the clays, and they contain some bizarre and fascinating new features, like the newberries."

Although Squyres stopped short of identifying the Whitewater Lake unit as being from Noachian Period, he did say it is "probably" Noachian. "We're still in the process of narrowing down the processes for how this stuff formed," he added.
"But I can say with near certainty that they are older than everything else we've seen."

If the Whitewater Lake unit is Noachian that means it was deposited some 3.7 billion to 4 billion years ago when Mars was warmer and wetter and more like Earth. It also means this is the furthest back into Mars' history that Opportunity has traversed.

Checking out Copper Cliff: This photograph shows Opportunity working away on Onaping, a target at the base of an outcrop called Copper Cliff on Matijevic Hill, in the west rim of Endeavour Crater. The rover snapped this picture with its front hazard-avoidance camera (Hazcam) on its Sol 3163 (Dec. 16, 2012). The outcrop is, once again, something new according to the MER science team. Image Credit: NASA / JPL-Caltech

At the end of 2012's last sol, Opportunity's work on locating the smectite helped make the last Earth year one of the best ever for the MER mission - and what has turned out to be a whole new mission at Endeavour Crater has only just begun. Beyond the ground-truthing of the sought-after phyllosilicates, "Matijevic Hill is one of the most interesting, puzzling and significant findings of the entire mission," said Squyres. "We have a lot more work to do here."

Meanwhile, Opportunity finished downlinking the last of the images for the Matijevic Panorama, which is now being processed by Jim Bell, panoramic camera (Pancam) lead, of Arizona State University (ASU). And, after completing an in-depth examination of a second Whitewater Lake rock in December, the rover scooted just up hill to a new, strangely alluring outcrop the team nicknamed Copper Cliff that looks something like an "organic" bench on which one could sit. "It's clearly a breccia - kind of a mix of rock fragments and matrix - but it also has a few of these newberries in it," said Arvidson.

There, Opportunity and her science team saw "a very clear and abrupt contact" between the Whitewater Lake unit and the Copper Cliff material, which is "sitting on top of it," said Squyres. "It is a major finding, but there's more work to be done," he said.

That contact was the first of what likely will be several key boundary discoveries that will inform MER science team members and help them sort out the layers - and geologic history - at Matijevic Hill and Endeavour Crater.

As 2013 got underway, Opportunity continued its investigations at various individual targets on an upper section of Copper Cliff the team dubbed Vermilion, taking close-up pictures with its microscopic imager and then analyzing its chemical composition with its alpha particle X-ray spectrometer (APXS). "It's another recessive bright bedrock that is kind of tilted up the hill," Arvidson said.

"Vermilion is very fine-grained, and has newberries and what appear to be breccia fragments," Arvidson continued. "It has a very low iron content and a composition different than anything we've seen. You can't make it by mixing any combination of Whitewater Lake and Shoemaker Formation materials, so again it's an unusual rock - and something different."

Newberries still a Martian mystery: Opportunity used its microscopic imager (MI) last September to take the pictures that went into this up-close mosaic, which may be one of the most important pictures on the MER mission, according to Principal Investigator Steve Squyres. The photograph combines four images and the view covers an area about 6 centimeters (2.4 inches) across, at the Kirkwood outcrop in the Cape York segment of the western rim of Endeavour Crater. Image credit: NASA / JPL-Caltech / processed by Stuart Atkinson

The MER science team members have their work cut out for them. In addition, to finding the contact between the Shoemaker Formation breccia rocks and the oldest-to-date Whitewater Lake unit, the scientists are still looking to analyze the tiny veins in the Whitewater Lake rocks, as well as the larger veins like the gypsum-rich Homestake that the rover found cutting through the bedrock in the apron around Cape York back in December 2011. And, among various other things, they still have to figure out what the newberries are. "We have multiple hypotheses about the newberries, but haven't proven or disproved any of them yet, because we haven't gone back to look at them again" said Squyres.

While Curiosity is still working to get her scientific "legs," Opportunity is cruising now toward her 9th anniversary of roving Mars, coming up January 24th. Producing more than half her full capability of solar power under typically hazy Martian spring skies, the MER is still proudly displaying its mettle.

"It's wonderful," said, John Callas, MER project manager at the Jet Propulsion Laboratory (JPL), home to the American Mars rovers. "I ran out of superlatives for Opportunity a long time ago."

After weeks of searching, the Mars rover Curiosity's science and engineering teams have selected a fine-grained slab of Martian rock as the candidate target for the first rock drilling on Mars, a significant first in planetary exploration.